| More attention on outer hair cells (OHCs) and their efferent nerve system have been paid previously in the investigations on noise induced hearing loss (NrHL) ,whereas little comprehension has been gained on the mechanism of the damage in the cochlear afferent nerve. The objective of the present experiment was to investigate the damage of cochlear afferent nerve endings underlying inner hair cells (llICs) caused by noise exposure through observing the changes of cochlear potentials and cochlear morphology, and then to explore the mechanism of excitotoxic disruption caused by excessive neurotransmitter glutamate in the cochlea through observing the changes of glutamate-like immunoreactivity (Glu- IR) of IHCs in guinea pigs. The present experiment included the following three parts. Part 1. To establish the method of semithin sections through the organ of Corti in guinea pigs At the present, the methods of cochlear paraffin embed section, glutin embed-freeze section, and celloidin embed section are used in most of research on cochlear morphology. However, these slicing methods have various disadvantages: Paraffin embed section is prone to dislocate the cells, glutin embed-freeze section coil the slices and celloidin embed section leave thicker slices with a longer processing time. For above reasons, these methods did not meet the requiremenis ln th1s experimeni. Therefore we established the semithinsection method for the organ of Corti in guinea pigs embeded w1th EPon812. Thestrucfore of coch1ear IHCs and OHCs and suPPorting cells can be clearlydisplayed after conventional dyeing, and the structhe of the organ of Corti wasnot damaged after inunnocytochemistry dyeing. Moreovef, this method needs1ess processing tlme with simPle and easy mbopulation. Conc1usion: Thesemithin section method of the organ of Corti in gUinea pig ls good for providinghigh qua1ity tissue s1ices.Part 2. The changes of the cochlear potential and the cochlearmorphology in guinea pigs after noise exposureThirty-eigh healthy guinea pigs were used. The animals were random1ydistributed into 5 grouPs: l conitol grouP and 4 experimCllal grouPs. Theexperimenal grOuPs inchided the grouP of 8 hours, one day three days and 7 daysafter noise exposure. In the experiment, the chronic round window electrodeswere 1mPlaned in the left bulla of all animals. Their righ eardIum were brokenand their nght outerear channel were blocked. The experimotal animals wereexposed to 120 dB SPL one third octave 4 kHz narrow band noise for 4 hours soas to induce the left cochlea daxnaged animal model by noise. Themeasurements of cochlea microphonics (CM) amP1itUde and comPound actionpotent1al (CAP) threshO1d of the left ear were made before and at the eachschedu1ed time after noise exposure. TWo gUinea pigs from each grouP wereused to observe the morpho1ogical changes in IHCs and OHCs of the organ ofCorti and the nerve endings underytng them. The results 1ndcated that afternoise exposure, the nonlinear property of CM inPul-outPut fimtion was reducedand CAP threshold were s1ghficanly increased in left ears (P<0.0l by paired ttest). There were vacuolization formation in plasma of OHCs and the affeentendings underlytng mCs after no1se exposure. As time passed, the above changeswere gradually alleviated. Our concluslon is that not only OHCs, bat also theaffernt nerve endings underlytng IHCs can be imPalred after noise exposure.Part 3. The changes of Glu-IR in cochlear IHCs after noise exposurehi order to explore the in jUIy mechAnsm of the afferent nerve endingsunderytng cochlear mCs, the teclmique of hauncytochendstry combined with.imrnungold technology was adopted. The Glu-IR in cochlear mCs wereobserv... |
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